This invention relates to a control device for an electrostatic precipitator having several filter chambers connected in series to one another.
Many industries such as the cement industry produce as by-products dust laden effluent gases which have to be cleaned before they are discharged to the atmosphere. Sometimes it is desirable to recover the dust also because of the inherent commercial value thereof. Electrostatic precipitators have been found to be a particularly cost-effective means of removing particles from effluent gases.
An electrostatic precipitator essentially comprises at least one electrical discharge electrode energizable to a high negative potential and at least one collector surface which is grounded. The gas to be cleaned flows between the discharge electrode and the collector surface. An electrical corona discharge from the discharge electrode causes the dust particles in the gas stream to acquire negative electrical charges while the electrostatic field causes the negatively charged particles to move towards and to be collected upon the grounded collector surface. The agglomerated dust particles are periodically removed from the collector surface by means of a recurrent rapping of the collector surface.
The discharge electrodes are usually wires or spiked rods maintained at the required negative potential by means of an electrical transformer and rectifier set.
Where a plurality of filter chambers are connected in series to one another, each filter chamber may be provided with an associated control element including an electrical transformer and rectifier set for generating between the electrodes of each filter chamber electrostatic fields for the collection of dust particles from a stream of air flowing from one filter chamber to the next in the interconnected series.
As described in European Patent Application No. 35,209, a pilot computer may be provided for modifying control variables as a function of the difference between a desired particle density of the outflowing gases at the output of the series of filter chambers and the actual particle density of the gases at the precipitator output, the control variables being fed in the form of electrical signals to the filter control of each filter chamber. A microcomputer system connected to the pilot computer via a coupling member and a data bus is associated with each filter or filter chamber for controlling the operation thereof. The pilot computer is programmed for calculating optimal electrical field strength in the individual filter chambers.
As set forth in German Patent Document (Deutsche Offenlegungsschrift) No. 29 49 797, the particle density of the gas at the output of a precipitator is detected by a particle density measuring device or sensor. The electrodes of a plurality of filter chambers in the precipitator are energized in such a matter as to attain the desired degree of separation with a minimum consumption of energy.
An object of the present invention is to provide an improved control device for an electrostatic precipitator.
Another object of the present invention is to provide such a control device with a pilot computer of improved design such that the particle density of the effluent gases at the output of the precipitator are brought as closely as possible in alignment with a preset reference value.
Yet another object of the present invention is to provide such a control device with a pilot computer which is adaptable to essentially all modes of operation existing in practice.